package title;

import java.util.Scanner;

/**
 * 功能：
 * 作者：lc
 * 日期：2024/11/28 22:55
 */
public class MainP5708 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double a = scanner.nextDouble();
        double b = scanner.nextDouble();
        double c = scanner.nextDouble();
        double p = (a + b + c) / 2;
        double d = p*(p - a) * (p - b) * (p - c);
        double result = Math.sqrt(d);
        System.out.printf("%.1f",result);
    }
}
